Activity: File Handling

Brief Intro — File Handling

Normally, a program loses all its data as soon as it closes, but files allow you to save information permanently on a disk. C provides powerful tools to create, read, and write files, ensuring your data survives even after the computer is turned off.

In this activity, you will learn how to use the FILE pointer and various opening modes so you can manage persistent data in your own C programs.

Task 1: File & File Handling

A file is a container in computer storage devices used for storing data. File Handling is the storing of data in a file using a program. C programs store results and other data to a file, and can extract/fetch data from a file to work with it in the program.

Task 2: Why Files?

• When a program terminates, the entire data is lost — storing in a file preserves it.
• Entering a large amount of data takes time; a file lets you access all the contents with a few commands.
• You can easily move data from one computer to another without any changes.

Task 3: Text vs Binary Files

Text files are normal .txt files: contents are plain text, easy to edit or delete, minimum effort to maintain, easily readable, provide the least security, and take bigger storage space. Binary files (mostly .bin) store data in binary form (0's and 1's): they hold a higher amount of data, are not readable easily, and provide better security.

Task 4: Four File Operations

In C you can perform four major operations on files, either text or binary:

1. Creating a new file
2. Opening an existing file
3. Closing a file
4. Reading from and writing information to a file

Task 5: The FILE Pointer

When working with files, you need to declare a pointer of type FILE. This declaration is needed for communication between the file and the program:

FILE *fptr;

Task 6: Opening a File — fopen()

Opening a file is performed with the fopen() function defined in stdio.h:

ptr = fopen("fileopen", "mode");

For example, fopen("C:\program.txt", "w") creates the file (if absent) and opens it for writing; fopen("C:\oldprogram.bin", "rb") opens an existing binary file for reading. The writing mode lets you create and edit (overwrite) contents; the reading mode only lets you read — you cannot write into the file.

Task 7: Opening Modes Table

Use the Explorer above. Key modes:

▶ Try it: Write Mode

• r / rb — open for reading; if the file does not exist, fopen() returns NULL.
• w / wb — open for writing; overwrites existing contents, or creates if absent.
• a / ab — open for append; data added to the end; creates if absent.
• r+ — open for reading and writing; returns NULL if the file does not exist.

Task 8: Closing a File

The file (both text and binary) should be closed after reading/writing, using the fclose() function:

fclose(fptr);

Here, fptr is the file pointer associated with the file to be closed.

Task 9: fprintf / fscanf

For reading and writing to a text file, we use fprintf() and fscanf(). They are just the file versions of printf() and scanf(). The only difference is that they expect a pointer to the structure FILE.

Task 10: Write Example Trace

The write program: declare FILE *fptr;, fptr = fopen("program.txt","w");, guard with if(fptr == NULL) { printf("Error!"); exit(1); }, then scanf("%d",&num);, fprintf(fptr,"%d",num);, and fclose(fptr);. The integer you entered is stored in the text file.

▶ Try it: Write 55

Task 11: Read Example Trace

The read program: fopen("program.txt","r") (exit if NULL), fscanf(fptr,"%d", &num);, then printf("Value of n=%d", num);, and fclose(fptr);. It prints the integer stored earlier.

Task 12: Read All + Binary Note

To read an entire file character by character, use fgetc(fp) in a while(1) loop, breaking when ch == EOF:

while ( 1 ) {
    ch = fgetc(fp);
    if ( ch == EOF )
        break;
    printf("%c", ch);
}

Other functions like fgetchar(), fputc() can be used in a similar way. For binary files, fread() and fwrite() are used for reading from and writing to a file on the disk.